Systems, devices, and methods for maintaining a secure audiovisual data link with an audiovisual sink during a switching event

ABSTRACT

When switching sources, resolutions or refresh rates in a video distribution network, switching times are reduced by maintaining video lock and security authentication between a video switcher and a video sink. The scaler maintains video lock and security authentication by continuing to generate video timing data during switching events. The scaler also facilitates an aesthetically pleasing transition by generating image content data prior to and after the switching event.

PRIORITY INFORMATION

The present application claims priority under 35 U.S.C. §120 as aContinuation patent application to U.S. Non-Provisional patentapplication Ser. No. 14/500,938 (client matter no. CP00190-02), filed 29Sep. 2014, which claims priority to U.S. Provisional Patent ApplicationSer. No. 61/883,719, under 35 U.S.C. §119(e), filed 27 Sep. 2013 (clientmatter no. CP00276-00), and which also claims priority under 35 U.S.C.§120 as a Continuation-in-Part patent application to U.S.Non-provisional patent application Ser. No. 13/764,315 (client matterno. CP00190-01), filed 11 Feb. 2013, which claims priority under 35U.S.C. §119(e) as a Non-provisional patent application to U.S.Provisional Patent Application Ser. No. 61/597,448 (CP00190-U.S.), filed10 Feb. 2012, the entire contents of all of which are expresslyincorporated herein by reference, and is related to co-pending, co-filedU.S. Non-provisional patent application Ser. No. ______ (client matterno. CP00190-03), entitled “Systems, Devices, and Methods for Generatinga Substantially Continuous Stream of Audiovisual Data During a SwitchingEvent,” the entire contents of which are incorporated herein byreference.

BACKGROUND

Technical Field

Aspects of the embodiments relate generally to video distributionnetworks. More particularly, aspects of the embodiments are directed tosystems, methods, and modes for distributing video protected by adigital rights management scheme.

Background Art

Video distribution networks are increasingly common installations incommercial and residential facilities. Components of a videodistribution network are typically located throughout the facility andnetworked allowing video to be distributed from one or more video sourceto one or more video sinks. For example, a typical video distributionnetwork in a home may comprise a multitude of video sources, such asBlu-Ray disc players, media servers, DVD players, digital videorecorders (DVR), and cable boxes. These video sources may be centrallylocated such as in an equipment rack in a closet and distributed via achain of switches and repeaters to various video sinks, such astelevision displays, computer monitors and projectors, throughout thehome.

However, as the digital distribution of television, movies, and musicexpands, content providers are growing increasingly concerned about thesimplicity with which content pirates can copy and share copyrightedmaterial. Various digital rights management (DRM) schemes have beendeveloped to ensure that television shows, movies and music can only beviewed or heard by authorized parties (i.e. paying customers). One DRMscheme to protect digital content as it is transmitted over cablesbetween devices is known as High-Bandwidth Digital Content Protection(HDCP). HDCP is a specified method developed by Digital ContentProtection, L.L.C. (DCP) for protecting copyrighted digital content asit travels across connection interfaces and protocols such asDisplayPort (DP), Digital Video Interface (DVI), High-DefinitionMultimedia Interface (HDMI). The HDMI specification defines an interfacefor carrying digital audiovisual content from a source such as a Blu-RayDisc player, to a sink or display device such as a television (TV).

There are three facets to HDCP. First, there is the authenticationprotocol, through which a source verifies that a given sink is licensedto receive HDCP content. With the legitimacy of the sink determined,encrypted HDCP content may be transmitted between the two devices, basedon shared secrets established during the authentication protocol. Theuse of such shared secrets prevents eavesdropping devices from utilizingthe content. Finally, in the event that legitimate devices arecompromised to permit unauthorized use of HDCP content, renewabilityallows a source to identify such compromised devices and prevent thetransmission of HDCP content.

The HDCP authentication protocol is an exchange between an HDCPcompliant source and an HDCP compliant sink that affirms to the sourcethat the sink is authorized to receive HDCP content by demonstratingknowledge of a set of secret device keys by transmitting a key selectionvector (KSV). Each HDCP device is provided with a unique set of thesesecret device keys, referred to as the device private keys (DPKs), fromDCP. The communication exchange also provides for both the HDCPcompliant source and sink to generate a shared secret value that cannotbe determined by eavesdropping on that exchange. By having that sharedsecret information embedded into the demonstration of authorization, theshared secret can then be used as a symmetric key to encrypt HDCPcontent intended only for the authorized device. Thus, a communicationpath is established between the HDCP source and HDCP sink that onlyauthorized devices can access.

In order for an HDCP compliant source to successfully transmit protectedcontent to one or more HDCP compliant sinks through an HDCP compliantrepeater, a more involved authentication process must first occur. Toaffirm the downstream sinks to the upstream sources, the HDCP repeatermust pass along the KSVs of each downstream receiver to the upstreamsource. The HDCP source checks these KSVs against an HDCP RevocationList maintained by DCP, LLC (“HDCP blacklist”) in order to determine ifeach of the downstream sinks are licensed to receive the protectedcontent. If all the downstream sinks are determined to be licensed toreceive the protected content, the upstream source transmits theprotected content to the HDCP repeater. It is the responsibility of theHDCP repeater to then establish and periodically manage authenticatedlinks with each of its connected HDCP receivers.

While HDCP offers the benefit of encrypted content transmission, therequired authentication protocol increases the switching delay in videodistribution networks. Each time a new path for video distribution isdesired, the links forming those paths must be authenticated. Forexample, when a user desires to switch to a different video source, notonly must the new video source authenticate with the repeater, but therepeater must also re-authenticate with the video sink. Increasedswitching times are disrupting and bothersome to users. In complex videodistribution systems with multiple layers, this problem is even moreamplified. Additionally, because HDCP scheme operates under the surface,most users do not realize that the increased time is the result of copyprotection schemes and often unfairly attribute them to the individualcomponents in the video distribution network.

An additional factor in the high switching delay in video distributionunits, is caused by the need for processing in video distributionnetworks. Scalers are employed to change the resolution or refresh rateof distributed video and are common components in video distributionnetworks, either as separate components or integrated into othercomponents in the network. Each time a video scaler receives audiovisualdata at a new resolution, there is a delay before the scaler outputs anynew video. The video scaler must load data and format before outputtingscaled video. This is known as achieving video lock. During a switchingevent, each scaler in the distribution path must achieve video lock insuccession. In complex video distribution systems with multiple layers,this delay is amplified.

Additionally, dependent on the characteristics of the display, viewersmay be subjected to disrupting video artifacts or snow during switches.Manufacturers handle disrupted video in different ways. Some displaysmay show snow when video is disrupted. Other may display pixilatedimages or ghost images. Many viewers find these display responsesdisturbing and lead some to believe that there is a problem with theirequipment when no such problem exists. Users may experience theauthentication process as a delayed period with snow or disorientingvideo artifacts.

There is now a need for an improved switcher for use in a videodistribution network. Accordingly, it would be desirable to providemethods, modes, and systems for distributing video protected by adigital rights management scheme.

SUMMARY

An object of the embodiments is to substantially solve at least theproblems and/or disadvantages discussed above, and to provide at leastone or more of the advantages described below.

It is therefore a general aspect of the embodiments to provide systems,methods, and modes for programming a control network and morespecifically for programming a control network comprising one or morelighting, shade, and other types of controllable devices that willobviate or minimize problems of the type previously described.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Further features and advantages of the aspects of the embodiments, aswell as the structure and operation of the various embodiments, aredescribed in detail below with reference to the accompanying drawings.It is noted that the aspects of the embodiments are not limited to thespecific embodiments described herein. Such embodiments are presentedherein for illustrative purposes only. Additional embodiments will beapparent to persons skilled in the relevant art(s) based on theteachings contained herein.

Aspects of the embodiments seek to overcome or at least ameliorate oneor more of the several problems described above, including but notlimited to: reducing the switching delay of a video distribution networktransmitting video.

According to a first aspect of the embodiment, a device and method areprovided for reducing the actual and perceived switching time of a videodistribution network by outputting a continuous stream of audiovisualdata including a repeated frame of image content data on a downstreamconnection of a switcher device.

According to a second aspect of the embodiments, a switcher devicecomprises at least two input boards, a multiplexer and an output board.Each of the at least two input boards are configured for receivingaudiovisual data from a video source. The multiplexer is communicativelycoupled between the at least two input boards and a transmitter boardand configured for dynamically routing audiovisual data from the atleast input boards to the transmitter board. The output board isconfigured for transmitting audiovisual data comprising a repeated frameof video to a video sink.

According to a third aspect of the embodiments, a switcher devicecomprises at least two input boards, a multiplexer board and an outputboard. Each of the at least two input boards is configured for receivingaudiovisual data from a video source. The multiplexer board comprises amultiplexer communicatively coupled between the at least two inputboards and an output board and configured for dynamically routingaudiovisual data from the at least two input boards to the output boardand a processing unit in communication with the multiplexer and theoutput board and configured for transmitting a switch signal to themultiplexer and a prepare signal to the transmitter board prior to aswitching event. The output board is configured for transmittingaudiovisual data to a video sink and comprises a receiver configured forreceiving audiovisual data routed from the multiplexer, a scalerconfigured for converting audiovisual data received via the multiplexerto video to a native resolution of the video sink, generating videotiming data at the native resolution of the video sink during theswitching event and generating image content data comprising a repeatedframe of video for a period of time until achieving video lock inresponse to receiving the prepare signal, and a transmitter configuredfor encrypting and transmitting generated audiovisual data to the videosink.

According to a fourth aspect of the embodiments, an output board for aswitcher device is adapted to transmit audiovisual data to a video sink.The output board comprises a receiver, a scaler and a transmitter. Thereceiver is configured for receiving audiovisual data. The scaler isadapted to convert the audiovisual data to a native resolution of thevideo sink and adapted to generate audiovisual data comprising arepeated frame during a switching event. The transmitter is furtheradapted to encrypt and transmit the output of the scaler.

According to a fifth aspect of the embodiments, a method is provided forreducing switching delay when switching sources in a video distributionnetwork. The method comprises the steps of receiving audiovisual data ata first input board from a first video sink, routing audiovisual datafrom the first input board to an output board, transmitting audiovisualdata from the output board to a video sink, receiving a user controlsignal to switch to a second video source, generating video timing dataat the output board during a delay between receiving audiovisual datafrom the first input board and receiving audiovisual data from thesecond input board to maintain authenticity of security protocol linkbetween the output board and the video sink, generating image contentdata at the output board during a delay between receiving audiovisualdata from the first input board and achieving video lock withaudiovisual data from the second input board, receiving audiovisual dataat a second input board from a second video sink, routing audiovisualdata from the second input board to the output board, and transmittingaudiovisual data from the output board to the video sink.

According to a sixth aspect of the embodiments, a computer programproduct is provided for reducing the switching time in a videodistribution network, the computer program product comprising a computerreadable storage medium having computer readable code embodiedtherewith. The computer readable program code comprises computerreadable program code adapted to detect a user control signal to switchfrom a first video source to a second video source, transmit a preparesignal to a processing unit of an output board in response to thedetection of the user control signal, detect the prepare signal,instruct a scaler to generate audiovisual data comprising image contentdata further comprising a repeated frame of video in response to thedetection of the prepare signal, cease routing audiovisual data from afirst video source to the output board, continue generating video timingdata at the scaler of the output board, begin routing audiovisual datafrom a second video source to the input board, and cease generatingimage content data upon achieving video lock.

According to a seventh aspect of the embodiments, a switcher device isprovided, comprising: at least one output board; at least two inputboards, each of the at least two input boards adapted to receiveaudiovisual data from a respective audiovisual source via a respectiveaudiovisual link; a multiplexer communicatively coupled between the atleast two input boards and the at least one output board, and adapted todynamically switch audiovisual data from the at least two input boardsto the at least one output board; and a switcher device processing unitadapted to notify the at least one output board that it will receive anoutput from the multiplexer a predetermined amount of time prior totransmitting a switch signal to the multiplexer for a switching event.

According to the seventh aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data from a firstaudiovisual source to receiving audiovisual data from a secondaudiovisual source.

According to the seventh aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data at a firstresolution to receiving audiovisual data at a second resolution.

According to the seventh aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data at a first refreshrate to receiving audiovisual data at a second refresh rate.

According to the seventh aspect of the embodiments, the at least oneoutput board comprises: an output board processing unit, and wherein theswitcher device processing unit is further adapted to transmit a preparesignal to the output board processing unit a predetermined amount oftime before transmitting a switch signal to the multiplexer for theswitching event.

According to the seventh aspect of the embodiments, the prepare signalcomprises: a network address of the at least output board.

According to the seventh aspect of the embodiments, the prepare signalis transmitted as a user datagram protocol packet.

According to the seventh aspect of the embodiments, the at least oneoutput board is adapted to (i) transmit audiovisual data to anaudiovisual sink via an audiovisual link, (ii) generate audiovisual datacomprising a repeated frame of image content data, and (iii) output asubstantially continuous stream of audiovisual data during the switchingevent, the audiovisual data comprising the repeated frame of imagecontent data, and wherein the at least one output board furthercomprises a scaler adapted to generate the repeated frame of imagecontent data during the switching event, and wherein the at least oneoutput board is adapted to transmit audiovisual data to the audiovisualsink via a security protocol link, and is further adapted to maintainthe security protocol link as an authenticated interface by generating acontinuous stream of video timing data during the switching event.

According to the seventh aspect of the embodiments, the scaler isfurther adapted to substantially continuously output the repeated frameof image content data until receiving a sufficient amount of audiovisualdata after the switching event to achieve video lock.

According to the seventh aspect of the embodiments, the scaler isfurther adapted to determine the native resolution of the audiovisualsink from Extended Display Identification Data (EDID) information of theaudiovisual sink.

According to the seventh aspect of the embodiments, the securityprotocol link is a High-bandwidth Digital Content Protection (HDCP)link.

According to the seventh aspect of the embodiments, the scaler isfurther adapted to generate the substantially continuous stream of videotiming data at a native resolution of the audiovisual sink.

According to an eighth aspect of the embodiments, a video distributionnetwork is provided comprising: at least two audiovisual sources; atleast one output board; a multiplexer communicatively coupled to boththe at least two audiovisual sources and the at least one output board;and a switcher adapted to dynamically route audiovisual data from the atleast two audiovisual sources to the at least one output board throughthe multiplexer, and is further adapted to notify the at least oneoutput board that it will receive an output from the multiplexer apredetermined amount of time prior to transmitting a switch signal tothe multiplexer for a switching event.

According to the eighth aspect of the embodiments, the switching eventcan be one of a switch from receiving audiovisual data from a firstaudiovisual source to receiving audiovisual data from a secondaudiovisual source, a switch from receiving audiovisual data at a firstresolution to receiving audiovisual data at a second resolution, and aswitch from receiving audiovisual data at a first refresh rate toreceiving audiovisual data at a second refresh rate.

According to the eighth aspect of the embodiments, the switchercomprises a switcher device processing unit, and the at least one outputboard comprises an output board processing unit, and wherein theswitcher device processing unit is adapted to be communicatively coupledwith the multiplexer and the output device processing unit, and theswitcher device processing unit is further adapted to transmit a preparesignal to the at least one output board processing unit a predeterminedamount of time before transmitting a switch signal to the multiplexerfor the switching event.

According to the eighth aspect of the embodiments, the prepare signalcomprises: a network address of the at least one output board.

According to the eighth aspect of the embodiments, the switcher deviceprocessing unit and the output device processing unit arecommunicatively coupled via an Ethernet interface.

According to the eighth aspect of the embodiments, the prepare signal istransmitted as a user datagram protocol packet.

According to the eighth aspect of the embodiments, the videodistribution network further comprises: at least one audiovisual sink,and wherein the at least one output board is adapted to—becommunicatively coupled to the at least one audiovisual sink, transmitaudiovisual data to the at least one audiovisual sink via an audiovisuallink, receive the notification from the switcher, generate audiovisualdata comprising a repeated frame of image content data in response tothe notification, and output a substantially continuous stream ofaudiovisual data during the switching event, the audiovisual datacomprising the repeated frame of image content data.

According to the eighth aspect of the embodiments, the at least oneoutput board comprises: a scaler adapted to generate the repeated frameof image content data during the switching event, and wherein the atleast one output board is further adapted to transmit audiovisual datato the at least one audiovisual sink via a security protocol link, andis further adapted to maintain the security protocol link as anauthenticated interface by generating a substantially continuous streamof video timing data during the switching event.

According to the eighth aspect of the embodiments, the switcher isfurther adapted to determine a network topology of the videodistribution network.

According to a ninth aspect of the embodiments, an output board in aswitcher device for transmitting audiovisual data to a video sink isprovided, the output board comprising: an output board processing unit;and a scaler adapted to generate video timing data at a nativeresolution of the video sink and a repeated frame of image content dataduring a switching event, wherein the switcher device comprises aswitcher device processing unit, and a multiplexer, and wherein (a) theswitcher device processing unit is communicatively coupled with themultiplexer and the output board processing unit, and (b) the switcherdevice processing unit is adapted to notify the output board processingunit that it the output board will receive an output from themultiplexer a predetermined amount of time prior to transmitting aswitch signal the multiplexer for the switching event.

According to the ninth aspect of the embodiments, the switcher deviceprocessing unit is adapted to transmit a prepare signal to the outputboard processing unit a predetermined amount of time before transmittinga switch signal to the multiplexer for the switching event.

According to the ninth aspect of the embodiments, the output board isfurther adapted to transmit audiovisual data to the video sink via asecurity protocol link and is further adapted to maintain the securityprotocol link as an authenticated interface by generating a continuousstream of video timing data during the switching event.

According to the ninth aspect of the embodiments, the switching event isa switch from receiving audiovisual data at a first resolution toreceiving audiovisual data at a second resolution.

According to the ninth aspect of the embodiments, the switching event isa switch from receiving audiovisual data from a first source toreceiving audiovisual data from a second source

According to the ninth aspect of the embodiments, the switching event isa switch from receiving audiovisual data at a first refresh rate toreceiving audiovisual data at a second refresh rate.

According to the ninth aspect of the embodiments, the scaler is adaptedfor continuing to output the repeated frame of image content data untilreceiving a sufficient amount of audiovisual data after the switchingevent to achieve video lock.

According to the ninth aspect of the embodiments, the scaler determinesa native resolution of the video sink from Extended DisplayIdentification Data (EDID) information of the video sink.

According to a tenth aspect of the embodiments, a method for switchingaudiovisual sources in a video distribution network is provided, themethod comprising: (a) receiving first audiovisual data at a switchingdevice; (b) transmitting the received first audiovisual data from theswitching device to at least one audiovisual data sink; (c) receivingsecond audiovisual data during a switching event; (d) transmitting theswitched second audiovisual data to the at least one audiovisual datasink; and (e) generating a notification signal a predetermined amount oftime prior to the step of outputting the switched second audiovisualdata.

According to the tenth aspect of the embodiments, the steps of receivingfirst and second audiovisual data comprise: transmitting the first andsecond audiovisual data from an audiovisual source; receiving thetransmitted first and second audiovisual data at an input board in theswitching device; transmitting the received first and second audiovisualdata from the input board; and receiving the transmitted first andsecond audiovisual data from the input board at a multiplexer in theswitching device.

According to the tenth aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data from a firstaudiovisual source to receiving audiovisual data from a secondaudiovisual source.

According to the tenth aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data at a firstresolution to receiving audiovisual data at a second resolution.

According to the tenth aspect of the embodiments, the switching eventcomprises: a switch from receiving audiovisual data at a first refreshrate to receiving audiovisual data at a second refresh rate.

According to the tenth aspect of the embodiments, the steps ofoutputting first and second audiovisual data comprises: outputting thefirst and second audiovisual data from the multiplexer to an outputboard; and outputting the first and second audiovisual data from theoutput board to an audiovisual sink.

According to the tenth aspect of the embodiments, the method furthercomprises: determining that an audiovisual switching event will occur;transmitting a switch signal to the multiplexer; and notifying theoutput board that it will receive an output from the multiplexer apredetermined amount of time prior to transmitting the switch signal tothe multiplexer for the switching event.

According to the tenth aspect of the embodiments, the step of notifyingcomprises: receiving a control signal at a switcher device processingunit that indicates a switching event from the first audiovisual data tothe second audiovisual data; and transmitting a prepare signal to theoutput board from the switcher device processing unit prior to switchingfrom the first audiovisual data to the second audiovisual data.

According to the tenth aspect of the embodiments, the method furthercomprises: in response to receipt of the prepare signal, generatingaudiovisual data by a scalar in the output board comprising a repeatedframe of image content data during the delay between receiving the firstaudiovisual data and receiving the second audiovisual data.

According to the tenth aspect of the embodiments, the repeated frame ofimage content data comprises: image content data from the firstaudiovisual data.

According to the tenth aspect of the embodiments, the method furthercomprises: transmitting the audiovisual data to the audiovisual sink bythe output board using a security protocol link, and maintaining thesecurity protocol link as an authenticated interface by generating acontinuous stream of video timing data during the switching event.

According to the tenth aspect of the embodiments, the prepare signalcomprises: a network address of the output board.

According to the tenth aspect of the embodiments, the method furthercomprises: determining a video distribution network topology.

According to the tenth aspect of the embodiments, the method furthercomprises: determining a network path to the output device.

According to the tenth aspect of the embodiments, the method furthercomprises: scaling audiovisual data at the output device to a nativeresolution of the display.

According to the tenth aspect of the embodiments, the method furthercomprises: continuing to generate audiovisual data at the output deviceuntil an amount of audiovisual data sufficient to achieve video lock isreceived from the second audiovisual source.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying figures further illustrate aspects of the embodiments.

The above and other objects and features of the embodiments will becomeapparent and more readily appreciated from the following description ofthe embodiments with reference to the following figures, wherein likereference numerals refer to like parts throughout the various figuresunless otherwise specified.

FIG. 1 is a block diagram of a high-bandwidth digital content protection(HDCP) system.

FIG. 2 is a block diagram of an HDCP system wherein two or more HDCPdevices are interconnected through at least one HDCP-protectedInterface.

FIG. 3 is a block diagram of an inventive switcher device according toaspects of the embodiments.

FIG. 4 is a block diagram of the switcher device shown in FIG. 3,according to aspects of the embodiments.

FIG. 5 shows a video distribution network, according to aspects of theembodiments.

FIG. 6 is a block diagram of the output board shown in FIG. 5, accordingto aspects of the embodiments.

FIG. 7 is a flowchart illustrating steps in a method for reducing theswitching time in a video distribution network, according to aspects ofthe embodiments.

FIG. 8 is a block diagram of a switcher device and extended transmissionboard, according to aspects of the embodiments.

FIG. 9 is a flowchart illustrating steps in a method for reducing theswitching time in a video distribution network, according to aspects ofthe embodiments.

FIG. 10 is a block diagram of a video distribution system, according toaspects of the embodiments.

FIG. 11 is a flowchart illustrating steps in a method for reducing theswitching time in a video distribution network, according to aspects ofthe embodiments.

FIG. 12 is a block diagram of a scaler, according to aspects of theembodiments.

DETAILED DESCRIPTION

The embodiments are described more fully hereinafter with reference tothe accompanying drawings, in which embodiments of the inventive conceptare shown. In the drawings, the size and relative sizes of layers andregions may be exaggerated for clarity. Like numbers refer to likeelements throughout. The embodiments can, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the inventive concept to those skilled in the art.The scope of the embodiments is therefore defined by the appendedclaims.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the embodiments. Thus, the appearance of thephrases “in one embodiment” on “in an embodiment” in various placesthroughout the specification is not necessarily referring to the sameembodiment. Further, the particular feature, structures, orcharacteristics can be combined in any suitable manner in one or moreembodiments.

LIST OF REFERENCE NUMBERS FOR THE MAJOR ELEMENTS IN THE DRAWING

The following is a list of the major elements in the drawings innumerical order.

-   100 High-Bandwidth Digital Content Protection (HDCP) System-   102 Interface Cable or Link-   104 Audiovisual (AN) Source-   106 A/V Sink/Display-   108 Secret Device Keys-   200 High Bandwidth Digital Content Protection System-   202 HDCP Content (Audiovisual Data)-   210 Control Function-   212, 215 HDCP Transmitter-   214, 216 HDCP Receiver-   219 Repeater-   220 Central Processing Unit (CPU)-   300 Video Distribution Network-   302 Switcher Device-   304 Control Signal-   306 Multiplexer-   308 Input Board-   310 Output Board-   316 User Control Signal-   318 Switcher Processing Unit-   320 Transceiver-   322 Control System-   323 User Interface Device (Wireless/Mobile Device)-   324 User Interface Device-   401 Receiver-   402 Output Scaler-   403 Output Processing Unit-   502 Interface Cable (Link)-   508 Extended Reception Board-   510 Extended Transmission Board-   601 Receiver-   615 HDCP Transmitter-   700 Method for Reducing the Switching Time in a Video Distribution    Network-   701-715 Steps of Method 700-   900 Method for Reducing the Switching Time in a Video Distribution    Network-   901-915 Steps of Method 900-   1100 Method for Reducing the Switching Time in a Video Distribution    Network-   1101-1116 Steps of Method 1100-   1201 Input Audiovisual Data-   1202 Frame Rate Processing Block-   1204 Memory-   1205 Output Audiovisual Data-   1206 Input Scaling Block-   1208 Output Scaling Block-   1210 Free-Running Output Timing Generator-   1211 Output Video Timing Data

LIST OF ACRONYMS IN THE SPECIFICATION

-   The following is a list of the acronyms used in the specification in-   alphabetical order.-   A/V Audiovisual-   API Application Programming Interface-   ASIC Application Specific Integrated Circuit-   CAT5e Category 5 Enhanced-   CD Compact Disk-   CPU Central Processing Unit-   DC Direct Current-   DCP Digital Content Protection, LLC-   DDC Display Data Channel-   DDWG Digital Display Working Group-   DM DigitalMedia-   DP DisplayPort Protocol-   DPDT Double Pole Double Throw-   DPK Device Private Keys-   DPST Double Pole Single Throw-   DRM Digital Rights Management-   DVD Digital Video Disc-   DVD Digital Versatile Disk-   DVI Digital Video Interface-   DVR Digital Video Recorder-   EDID Extended Display Data Channel-   FPGA Field Programmable Gate Array-   HDCP High-Bandwidth Definition Content Protection-   HDMI High Definition Multimedia Interface-   HPD Hot Plug Detection-   KSV Key Selection Vector-   LCD Light Commanding Diode-   PCB Printed Circuit Board-   RAM Random Access Memory-   ROM Read Only Memory-   SDK Software Development Kit-   SPDT Single Pole Double Throw-   SPIF Serial Peripheral Interface-   SPST Single Pole Single Throw-   STP Shielded Twisted Pair-   TMDS Transition Minimized Differential Signaling-   TV Television-   UDP User Datagram Protocol-   UTP Unshielded Twisted Pair

LIST OF DEFINITIONS

Authorized device—An HDCP device that is permitted access to HDCPcontent. An HDCP transmitter may test if an attached HDCP receiver is anauthorized device by successfully completing the first and, whenapplicable, second part of the authentication protocol. If theauthentication protocol successfully results in establishingauthentication, then the other device is considered by the HDCPtransmitter to be an authorized device.

Downstream—Term used as an adjective to refer to being towards thesink/display of the HDCP content stream.

DVI—Short for Digital Video (or Visual) Interface, a digital interfacestandard created by the Digital Display Working Group (DDWG) toaccommodate both analog and digital monitors.

HDCP—short for High-Bandwidth Digital Content Protection, a specifiedmethod developed by Digital Content Protection, L.L.C. (DCP) forprotecting copyrighted digital content as it travels across connectioninterfaces and protocols such as DisplayPort (DP), DVI, and HDMI, amongothers.

HDCP content—consists of audiovisual content that is protected by theHDCP system. HDCP content includes the audiovisual content in encryptedform as it is transferred from an HDCP transmitter to an HDCP receiverover an HDCP-protected Interface.

HDCP device—Any device that contains one or more HDCP-protectedinterface ports and is designed in adherence to HDCP.

HDCP Encryption—The encryption technology of HDCP when applied to theprotection of HDCP content in an HDCP system.

HDCP-protected Interface—An interface for which HDCP applies.

HDCP-protected Interface Port—A connection point on an HDCP Device thatsupports an HDCP-protected Interface.

HDCP receiver—An HDCP device that can receive and decrypt HDCP contentthrough one or more of its HDCP-protected interface ports.

HDCP repeater—An HDCP device that can receive and decrypt HDCP contentthrough one or more of its HDCP-protected interface ports, and can alsore-encrypt and emit the HDCP content through one or more of itsHDCP-protected interface ports. An HDCP repeater may also be referred toas either an HDCP receiver or an HDCP transmitter when referring toeither the upstream side or the downstream side, respectively.

HDCP transmitter—An HDCP device that can encrypt and emit HDCP contentthrough one or more of its HDCP-protected interface ports.

HDMI—Short for High-Definition Multimedia Interface, anindustry-supported, uncompressed, all-digital audio/video interface.

Upstream—Term used as an adjective to refer to being towards the sourceof the HDCP content stream. The antonym of “downstream,” defined above.

FIGS. 1 and 2 illustrate examples of HDCP systems 100, 200. Referring toFIG. 1, the HDCP system 100 encrypts the digital content transmissionbetween a video source 104 (set-top box, computer, DVD, etc.) and a sinkor display 106 (liquid crystal display (LCD), television, etc.) via aninterface 102 such as DVI, HDMI, and DP interfaces, among others.

FIG. 2 illustrates an HDCP system 200 wherein two or more HDCP devices104, 106 are interconnected through an HDCP repeater and twoHDCP-protected Interfaces 102 a, 102 b (collectively 102). Eachpoint-to-point HDCP link involves one HDCP transmitter 212, and one HDCPreceiver 214. As such, the HDCP repeater 219 must decrypt the HDCPcontent at the HDCP receiver 216 on each of its inputs. The repeater 219must then re-encrypt the data with an HDCP transmitter 215 on each ofits outputs. According to an aspect of the embodiments, repeater 219must inform the upstream device of its downstream connection, andrepeater 219 has the responsibility to maintain those connections.According to further aspects of the embodiments, repeater 219 can informthe upstream device of its downstream connector, and repeater 219 canmaintain those connections. The audiovisual content protected by HDCP,HDCP content 202, flows from an upstream content control function 210into the HDCP system 200 at the most upstream transmitter 212. Fromthere, the HDCP content 202, encrypted by the HDCP system 200, flowsthrough a tree-shaped topology of HDCP receivers 214 over HDCP-protectedInterfaces 102. Before sending data, the each transmitter 212, 215checks that the HDCP receivers 214, 216 are authorized to receive theHDCP content 202. If so, the transmitter 212 encrypts the HDCP content202 to prevent eavesdropping as it flows to the receiver 216. A centralprocessing unit 220 includes firmware to process the data 202 and otherinformation and control.

Device manufacturers typically buy HDCP chips from a DCP-licensedsilicon vendor. These chips usually also provides transition minimizeddifferential signaling (TMDS) encoders or decoders and otherHDMI-specific features. Every transmitter 212 will have at least oneHDCP transmitter chip and every receiver 216 will have at least one HDCPreceiver chip. The HDCP transmitters 212, and receivers 216, frequentlyrequire a microprocessor to implement the authentication state machines.Transmitters 212, 215 are HDMI transmitters.

Authentication and Encryption Protocols

HDCP authentication consists of three parts:

Part One: The source 104 authenticates with the sink/display 106connected to its output. If successful, encryption is enabled andaudiovisual (NV) content transmission begins.

Part Two: This part is used if the downstream device is a repeater 219.The repeater 219 authenticates with the devices connected to itsoutput(s) and passes the HDCP tree topology information up to the source104. The source 104 is the root and sinks/display 106 are the leaves,while repeaters 219 make up the branches of the tree.

Part Three: The source 104 performs periodic checks with thesink/display 106 to ensure that encryption is in sync. As mentionedabove, it is the repeater's responsibility to maintain its downstreamconnections. If any part of authentication fails or any revoked devicesare found in the HDCP tree, the transmitter 212 must stop sendingprotected content and authentication starts over at Part One.

Authentication Part One

Part One of authentication is a key exchange protocol. The transmitter212 and receiver 216 calculate a common secret session key 108 to beused for encryption. If they cannot come up with the same key value,authentication fails and the receiver 216 will not be able to decryptthe content 202. The session key is derived from each device's privatekey according to the following protocol:

First, the transmitter 212 generates a random number “A_(n)” and sendsit to the receiver 216. This value will be used later in the protocol.The devices 104, 106 then exchange KSVs. The receiver 216 also sends itsREPEATER bit, a flag that indicates whether or not it is part of arepeater. Now each device 104, 106 has the other device's KSV. Eachdevice 104, 106 uses the other device's KSV to select twenty of its ownkeys. The forty bits in the KSV correspond to the indexes of each of theforty private keys. For every set bit in the received KSV, the localprivate key at that index is selected. All KSVs have twenty set bits, sotwenty keys are selected. The devices 104, 106 then each add up theirselected keys to come up with the sums Km and Km′, for the transmitterand receiver, respectively 212, 216. For authentication to succeed, Kmand Km′ must match. Each device 104, 106 tells the other which of itsown unique, secret keys to select, and they both come up with the samesum. That may seem counter-intuitive, but it is the aforementionedmathematical relationship between the keys and the KSVs that accountsfor this behavior. The source 104 must determine whether Km and Km′match. However, they are secret values, so they cannot be transmittedover the interface cable 102 for the DDC. Each device 104,106 feeds Km(or Km′), the random number “A_(n)”, and the REPEATER bit into theirrespective HDCP cipher engines in order for the transmitter 212 toverify that the values match without sending them across the cable 213for everyone to see. The resulting data stream is split into threevalues:

R0/R0′: This return value may be shared between the devices 104, 106 andis used to verify that authentication was successful.

Ks/Ks′: This value is kept private and is used as the encryption sessionkey for the HDCP cipher.

M0/M: This value is also kept private and is used in Part Two ofauthentication (if the downstream device is a repeater 219).

The receiver sends R0′ to the transmitter 212, which compares it againstits' own R0 value. If they match, that proves that the sums Km and Km′matched, and authentication is successful. Furthermore, the session keysKs and K match, so the receiver 214 will be able to decrypt the contentencrypted by the transmitter. If Part One of authentication wassuccessful, the transmitter 212 may begin sending encrypted content 202.If the downstream device is a repeater 219, the repeater 219 mustauthenticate with its own downstream device according to the sameprotocol. The transmitter 212 then starts a 5-second timer to allow forthe repeater 219 to perform Part Two of authentication. If Part Twofails or times out, authentication fails and the transmitter 212 muststop transmitting the protected content 202.

Authentication Part Two

Part Two of authentication only occurs if the downstream device is arepeater 219. The purpose of Part Two is to inform the source 104 of alldownstream devices and the HDCP tree depth. The source 104 uses thisinformation to ensure that the tree topology maximums have not beenexceeded and to ensure that none of the downstream devices have beenrevoked by DCP. The repeater 219 first assembles a list of the KSVs ofall downstream devices, as well as the device count and the tree depth.The repeater 219 then passes this information up to the source 104. Toensure that this information hasn't been tampered with duringtransmission, each device takes this list, appends its secret valueM0/M0′ from Part One, and calculates a SHA-1 hash of the whole thing.The transmitter 212 reads the hash result from the receiver 214 andcompares it against its own. If they match, Part Two of authenticationis successful.

Authentication Part Three

All HDCP devices are considered authenticated after successfulcompletion of Authentication Parts One and Two. Part Three is simply alink integrity check to ensure that encryption is in sync between alltransmitter/receiver pairs 212, 214, 215, 216 in the tree. To supportlink integrity checks, the return values Ri and Ri′ roll over to a newvalue every 128 frames. Recall that the initial Ri values R0 and R0′were generated during Part One of authentication. Every two seconds, thetransmitter 212 compares the receiver's 216 Ri′ value against its own Rivalue to see if they match. If they don't, encryption is out of sync andthe receiver 216 cannot correctly decrypt the content 202. The user willsee a scrambled or “snowy” image on the screen. In this case thetransmitter 212 must restart authentication from the beginning.

The three part authentication process increases switching delay whenswitching sources in a video distribution network. Switching delay isthe delay between switching an aspect of incoming audiovisual data to avideo sink, such as audiovisual data source, audiovisual data resolutionand audiovisual data refresh rate, and the incoming audiovisual databeing displayed on the video sink. Not only must devices authenticatethe HDCP link before video transmission, each time an upstream HDCP linkis switched, downstream HDCP links may be affected as well becauseaudiovisual data transmission to downstream links is interrupted. Eachtime video transmission is interrupted between an HDCP transmitter andan HDCP receiver, the HDCP link fails Part Three of the authenticationprocess and the authentication process must be restarted from Part One.This includes downstream connections that were previously authenticatedwith each other.

For example, in a video distribution network comprising a firstHDCP-compliant video source and a second HDCP compliant video sourceconnected to an HDCP compliant video sink via an HDCP compliant videoswitcher, when the video source transmitting HDCP content to the videosink is switched from the first video source to the second video source,not only must the second video source authenticate with the videoswitcher, but the downstream link between the video source and the videoswitcher must also be re-authenticated due to the disruption in videotransmission. This despite the fact that the HDCP link between the videosource and the video switcher was already authenticated. This issuebecomes increasingly burdensome in expansive video distribution networkswith many layers (i.e. a large tree topology).

Additionally, when video transmission is interrupted between an HDCPtransmitter and an HDCP receiver due to upstream switching and HDCPauthentication, any downstream video scalers must lock back on theincoming audiovisual data before outputting any scaled audiovisual data.This introduces delay in addition to the delay introduced by the HDCPauthentication process. For example, each time video transmission to asink is interrupted, video scaler internal to the sink will takeanywhere between two and ten seconds to lock onto the incomingaudiovisual data again. Those skilled in the art will recognize thatscaler operation is unpredictable and varies due to hardware andfirmware specification. Often, video scalers included in video sinks arenot optimized for reducing switching delay. Also unpredictable is videosink response while embedded video scalers achieve video lock. Presentedwith interrupted video, the video sink may display snow, pixilatedimages, video artifacts or a blank screen while internal scaler achievesvideo lock dependent on video sink manufacturer.

Because the HDCP authentication process operates in the background,often unknown to the user, long switching delays are unfairly blamed onvideo distribution components. Users may experience the authenticationprocess as a delayed period with snow or disorienting video artifacts.This could result in undeserved user dissatisfaction with themanufacturer of the components in the video distribution network.

As will be explained below, aspects of the embodiments describe systems,apparatuses and methods for reducing the switching time in a videodistribution network. Aspects of the embodiments described hereinprovide for maintaining authentication of downstream link during aswitching discontinuity, minimizing the interruption of videotransmission resulting from switching events. By outputting continuousvideo timing data to a sink over a downstream HDCP link, even duringswitching discontinuities, the downstream HDCP link satisfies themaintenance check in step three of HDCP authentication. Accordingly,steps one and two of the HDCP authentication protocol need not berepeated. Additionally, as a result of maintaining the authentication ofthe HDCP link by outputting continuous video timing data duringswitching discontinuities, video scalers downstream of the HDCP link(i.e., internal video sink scalers) will not lose video lock with theincoming video stream thereby reducing delay times further. Finally, byoutputting black frames of image data, the content displayed duringswitching events is controlled.

FIG. 3 is a block diagram of an inventive switcher device configured forreducing switching time in a video distribution network. The videodistribution network 300 is an HDCP system and includes at least onesource 104 a, 104 b, . . . , 104 n (collectively 104) and at least onesink or display 106 a, 106 b, . . . , 106 n (collectively 106). At leasttwo sources 104 include an HDCP transmitter 212, such as an HDMItransmitter, configured to transmit audiovisual data comprising videotiming data and image content data to the at least one sink 106. Eachsource 104 further includes a graphic generator (not shown) to generatea graphic or image. The HDCP transmitter 212 receives the HDCP content202 from an upstream content control function 210.

At least one sink includes an HDCP receiver, such as an HDMI receiver.The source 104 determines via the authentication process what contentcan be viewed, recorded, and shared based on sinks/displays 106 thatsupport HDCP and sinks/displays 106 that does not support HDCP. Theoutput of the source 104 is connected to an input board 308 for aswitcher device 302 through their HDCP-protected interfaces 304 and theswitcher device 302 serves as an HDCP repeater for HDCP compliantcontent. An output board 310 for the switcher device 302 is connected tothe input of the sink/display 106 via another interface 102 b. Theinterface 102 a, 102 b for the input board and the output board of theswitcher device 302 may be an HDMI cable that carries a variety ofsignals such as one or more of TDMS, DDC, hot plug detect (HPD), andRxSense, among others. As will be described later, the interface 102 a,102 b for the input board and output board of the switcher device 302may also be a combination of one or more shielded twisted pairs (STP)and one or more unshielded twisted pairs (UTP), such as DigitalMedia(DM) cable available from Crestron Electronics, Inc. of Rockleigh, N.J.

When an HDCP source 104 (more specifically source 104 a) detects anRxSense signal from an HDCP compliant sink/display 106 (morespecifically sink/display 106 a), the source 104 a will transmit HDCPcontent 202 to the sink/display 106 a after the authentication processis successful.

The audiovisual data 202 is encoded into three data channels. Thesechannels and a TMDS clock are carried over four differential pairs fromthe source 104 to the sink/display 106. The DDC is a communicationsinterface similar to I2C. This interface provides two-way communicationin a master-slave relationship. The upstream device 104 is the DDCmaster and the downstream device 106 is the DDC slave. The HDCP receiverindicates its presence to the HDCP transmitter with the HPD signal. TheHDCP transmitter 212 is the HDCP Device most upstream, and receives theHDCP content 202 from an upstream content control function 210.

The switcher device 302, functioning as an HDCP repeater, is a fullymodular and expandable matrix switcher offering low-latency digitalvideo and audio switching, and HD lossless multi-room signaldistribution, for all types of A/V sources. The switcher device 302 maybe a Crestron Digital Media Switcher available from CrestronElectronics, Inc. of Rockleigh, N.J.

The Crestron Digital Media Switcher is field-configurable to handle, butnot limited to, eight, sixteen, and thirty-two audiovisual sources ofvirtually any type via input boards. The outputs are alsofield-configurable to provide, but not limited to, eight, sixteen, andthirty-two room outputs and/or HDMI outputs in a single chassis. Thechassis comprises slots for the insertion of input and output boards. Aswill be described later, the input boards and output boards may be inputboards and output boards, respectively, of the switcher device 302.Additionally, the input boards and output boards may operate external ofthe chassis of the Digital Media Switcher and be coupled to the DigitalMedia Switcher via intermediate cards inserted into slots in thechassis.

The switcher device 302 includes a multiplexer 306 coupled in-betweenthe at least one input board 308 a, 308 b, 308 n (collectively 308) andat least one output board 310 a, 310 b, 310 n (collectively 310). Themultiplexer 306 may be, but is not limited to, a mechanical switch,electrically operated switch, solid state relay, latching relay, reedrelay, single-pole single-throw (SPST) relay, single-pole double-throw(SPDT) relay, double-pole single-throw (DPST) relay, and double-poledouble-throw (DPDT) relay.

The multiplexer 306 transmits an audiovisual data signal 202 from one ofthe at least two input boards 308 to a first output board 310 a. Themultiplexer 306 dynamically switches between the first input board 308 aand at least a second input board 308 b based on a user control signal316 that selects either the first video source 104 a or second videosource 104 b to be displayed on the video sink 106 a. The output board310 is coupled to the at least one sink/display 106 via an interfacecable 102 b. The interface cable 102 b may be an HDMI cable. Theswitcher 302 further includes a processing unit 318 coupled to themultiplexer 306. The processing unit 318 includes at least onetransceiver 320 for bidirectional communications with an end user device(e.g., 324, 326), in part, to receive the user control signal 316. Theend user device 324, 326 transmits the user control signal 316 from atouch panel display 324 via a control system 322. An end user may alsotransmit the user control signal 316 from a wireless device 326.Software tools 328 may be loaded onto the wireless device and/or touchpanel 324 to assist the end user in selecting a desired source 104 andthe sink 106. In response to the user selecting the desired source 104for the sink 106, the end user device transmits the user control signal316 to the switcher device 302.

Upon the user selecting the desired source 104 for the at least onedesired display 106, the source 104 will authenticate with the switcherdevice 302 as described above. The switcher device 302 will authenticatewith the at least one desired downstream sinks 106 as described above.Once the authentication is complete, the source 104 will transmit theHDCP content (i.e. HDCP protected audiovisual data) via the HDCP linkbetween the source and the repeater. This HDCP link comprises the HDCPtransmitter 212 of the source, an HDCP interface, and an HDCP receiver214 of the first input board 308 a. The HDCP receiver of the input board308 a receives the HDCP content and provides the audiovisual dataunencrypted to the multiplexer 306. The multiplexer 306, dependent onthe user control signal 316, routes the unencrypted audiovisual data tothe desired output board 310. The output board 310 processes andencrypts the audiovisual data and then transmits the HDCP content to thedesired sink 106 over an HDCP link between the output board 310 and thevideo sink 106. The HDCP link between the output board 310 and the videosink 106 comprises an HDCP transmitter 215 of the output board, HDCPinterface and HDCP receiver of the video sink.

The multiplexer 306 is configured to dynamically route the audiovisualdata according to the user control signal received at the processingunit 318. For example, a user viewing content from a first source 104 a,such as a cable tuner, may desire to switch to a second source 104 b,such as a Blu-ray disc player. When the multiplexer 306 switches fromrouting audiovisual data from the first source to routing audiovisualdata from the second source 104 b, the output board 310 experiences aswitching delay as a result of the delay caused by upstream HDCPauthentication and multiplexer 306 operation. A similar switchingdiscontinuity may also result from a change in resolution or change inrefresh rate of the received audiovisual data.

The output board 310 of the inventive switcher device 302 is configuredto continuously output audiovisual data including video timing data andimage content data during switching discontinuities such that the HDCPlink between the output board 310 and the video sink 106 remainsauthenticated during the switch and an aesthetically pleasing display isshown during said switch. For example, the output board 310 may outputblack frames of audiovisual data during switching discontinuities.Switching delay in the video distribution network 300 is minimized bymaintaining the authentication of the HDCP link by continuouslyoutputting video timing data. Additionally, by continuously outputtingvideo timing data to the video sink during switching discontinuities,video lock is maintained in video processing devices, such as scalers,downstream from the output board 310 (i.e. scalers internal to videosink), thereby further minimizing switching delay.

FIG. 4 is a block diagram of a portion of the switcher device 302 shownin FIG. 3. The output board 310 a further comprises a receiver 401, anoutput scaler 402, an output processing unit 403 and an HDCP transmitter215. The receiver 401 is configured to receive audiovisual data routedfrom the first input board 308 a or second input board 308 b via themultiplexer 306. As described below, according to aspects of theembodiments, the receiver 401 is an HDCP receiver configured forreceiving HDCP encrypted content.

The output scaler 402 receives the audiovisual data from the receiver401 and is adapted to convert the received audiovisual data to a nativeresolution of the video sink 106. The output board 310 may receive thenative resolution of the video sink 106 via an EDID channel. Thoseskilled in the art will recognize that the operation of video scalersembedded in end user devices are idiosyncratic depending on manufacturerand may perform substantially below par, resulting in poor video qualityand delayed performance. By converting to the native resolution of thevideo sink 106, video processing is minimized in downstream embeddedvideo scalers.

According to aspects of the embodiments, the output scaler 402 of theoutput board 310 is adapted for operating in a pass through mode inwhich the output scaler detects the resolution of the incomingaudiovisual data via the video timing data. The output scaler passes theincoming audiovisual data through to the HDCP transmitter if theaudiovisual data is routed to the output board already at a nativeresolution of the video sink.

The output scaler 402 is further adapted to generate audiovisual datacomprising video timing data and image content data during switchingdiscontinuities. For example, during a switching discontinuity betweenreceiving audiovisual data from a first source 104 a and audiovisualdata from a second source 104 b, the output scaler 402 may output blackframes. By outputting a continuous stream of audiovisual data, morespecifically video timing data, to the HDCP transmitter 215, the HDCPlink between the output board 310 and the source is maintained asauthenticated during the switch. In addition, by outputting black framesof audiovisual data, more specifically image content data, the end userexperiences a clean transition from the first source 104 a to the secondsource 104 b. According to aspects of the embodiments, the output scaler402 may generate frames of image content data of a color other thanblack, or may generate image content data comprising an image, such as acorporate logo.

According to aspects of the embodiments, prior to outputting audiovisualdata from the second source 104 b, the output scaler 402 must receive asufficient amount of audiovisual data from the second source 104 b. Thisis known as achieving video lock. Following a switching discontinuity,the output scaler 402 is further adapted to generate image content datauntil video lock is achieved. By generating image content data until theoutput scaler 402 achieves video lock, the user is presented with aclean transition during switching events.

The output scaler 402 is adapted to operate in a free run mode byautomatically generating video timing data during switchingdiscontinuities.

The output scaler 402 is adapted to generate image content data inresponse to control signals from the output processing unit 403. Uponreceiving the user control signal to switch the source of audiovisualdata and prior to transmitting a switching signal to the multiplexer306, the switcher processing unit 318 transmits a prepare signal to theoutput processing unit 403. The output processing unit 403 in turninstructs the output scaler 402 to generate black frames of audiovisualdata.

The HDCP transmitter 215, such as an HDMI transmitter, converts andencodes the audiovisual data output from the output scaler 402 to one ormore TMDS signals for transmission to the video sink 106 over the HDCPinterface. According to aspects of the embodiments, the HDMI transmittercomprises an HDCP transmitter chip and may further comprise TMDSencoders or decoders and other HDMI-specific features. The audiovisualdata is re-encrypted in accordance with the shared secret fromauthentication between the HCDP repeater and the HDCP sink. The HDCPtransmitter 215 receives the native resolution and the native refresh ofthe sink via a display data channel (DDC) of the interface. The HDCPinterface between transmitter and the HDCP receiver may be HDMI.

FIG. 5 shows the switcher device 302 in a video distribution network300, according to further aspects of the embodiments in which the outputboard 310 is contained in a housing external to the switcher device 302.The video distribution network 300 comprises an extended transmissionboard 510 coupled between the multiplexer 306 and the output board 310.The video distribution network 300 further comprises an extendedreception board 508. According to aspects of the embodiments, theextended reception board 508 and extended transmission board 510 may bemodular input and output boards, respectively, configured to be insertedinto the switcher device 302. As described below, the extendedtransmission and reception boards allow for extended cable lengths thatincreases the functionality of the video distribution network 300. Forexample, the output board 310 may be collocated in the same area as itscorresponding video sink 106. The switcher device 302 may be remotelylocated in a central location or out of view, such as in an equipmentcloset. Similarly, the first input board 308 a and second input board308 b may be collocated with the first video source 104 a and the secondvideo source 104 b, respectively.

According to aspects of the embodiments, the output board 310 is adaptedfor receiving encrypted audiovisual data via an HDCP link. The extendedtransmission board 510 is communicatively coupled between themultiplexer 306 and the output board 310 and is adapted for encryptingthe audiovisual data routed by the multiplexer 306 and transmitting theencrypted audiovisual data to the output board 310 via an HDCP link. TheHDCP link comprises an HDCP transmitter 615 of the extended transmissionboard 510, an HDCP interface 502 and an HDCP receiver 401 of the outputboard 310. The HDCP interface 502 may be one or more pairs of twistedcable or fiber optical cable, such as DigitalMedia cable available fromCrestron Electronics, Inc. of Rockleigh N.J. Those skilled in the artwill recognize that DigitalMedia cable is a multi-generational family ofinterface cables particularly designed for media transmission forextended lengths.

Within a single plenum-rated jacket, original DigitalMedia cablecontains one high-bandwidth/low-crosstalk shielded 4-twisted pair (STP)cable, one CAT5e unshielded 4-twisted pair (unshielded twisted pair(UTP)) cable, and one DMNet cable. The STP “Audiovisual data” cable isof a specialized construction designed to allow the longest possiblecable lengths for transporting high-definition digital video and audio.The Cat5e “Data Management” cable carries high-speed Ethernet and otherdata, plus 5V direct current (DC) power. Finally, the DMNet cablecarries additional proprietary control signals and 24V DC power.Original DigitalMedia cable is rated for up to 220 ft of audiovisualtransmission.

FIG. 6 is a block diagram of the extended transmission board and theoutput board shown in FIG. 5, according to aspects of the embodiments.The block diagram of the output board 310 is similar to the blockdiagram of the output board 310 in FIG. 4, with the exception being thatin FIG. 5, the receiver 401 is an HDCP receiver configured for receivingHDCP content over an HDCP interface 502. The extended transmission board510 comprises a receiver 601 and an HDCP transmitter 615.

FIG. 7 is a flowchart illustrating steps of method 700 for reducing theswitching time in a video distribution network 300, according to aspectsof the embodiments.

In step 701, a switcher device 302 receives audiovisual data at a firstinput board 308 a via an HDCP link between a first video sink 106 a andthe first input board 308 a.

In step 702, the switcher device 302 routes audiovisual data from thefirst input board 308 a to an output board 310 a.

In step 704, the output board 310 transmits audiovisual data to a videosink 106 over a security protocol link. According to aspects of theembodiments, the output board 310 scales the audiovisual data receivedfrom the first input board 308 a to the native resolution of the videosink 106 (step 703) prior to transmitting to the video sink 106.

In step 705, the processing unit 318 of the switcher device 302 receivesa control signal to switch from routing audiovisual data from the firstinput board 308 a to routing audiovisual data from the second inputboard 308 b.

According to aspects of the embodiments, the switcher device processingunit 318 transmits a prepare signal to the output board 310 a,indicating that there will be a switching discontinuity (step 706).

According to aspects of the embodiments, the output board 310 agenerates image content data, such as black frames of video, in responseto receiving the prepare signal from the switcher device processing unit318 (step 707). The scaler 402 outputs the generated image content datarather than the live image content data being routed to the output board310 a from the multiplexer 306.

In step 708, the multiplexer 306 ceases routing audiovisual data fromthe first input board 308 a.

In step 709, the output board 310 continues generating video timing dataat a native resolution during the delay between receiving audiovisualdata from the first input board 308 a and receiving audiovisual datafrom the second input board 308 b. By outputting a continuous stream ofvideo timing data, the output board 310 a maintains the authenticity ofthe security link between the output board 310 a and the video sink 106.

In step 710, the switcher device 302 receives audiovisual data at asecond input board 308 b via an HDCP link between a second video sink106 b and the second input board 308 b.

In step 711, the switcher device 302 routes audiovisual data from thesecond input board 308 b to the output board 310 a.

Following step 711 is decision step 715. In decision step 715, it isdetermined whether video lock has occurred. If video lock has occurred(“Yes” path from decisions step 715), method 700 proceeds to step 713.If video lock has not occurred (“No” path from decision step 715),method 700 proceeds to step 712, and continues to monitor video data todetermine if video lock has occurred.

In step 712, the output board continues generating and outputting imagecontent data (i.e. black frames of video) until video lock is achieved.

In step 714, the output board 310 a transmits live image content datarouted from the second input board 308 a to the video sink 106 over anHDCP link. According to aspects of the embodiments, the output board 310a scales the audiovisual data received from the first input board 308 ato the native resolution of the video sink 106 (step 713) prior totransmitting to the video sink 106.

The following is a pseudo-code representation of the operation inaccordance with aspects of the embodiments.

Detect a user control signal to switch from a first video source to asecond video source.

Transmit a prepare signal to a processing unit of an output board inresponse to the detection of the user control signal.

Detect the prepare signal at the output boar.

Instruct scaler to generate image content data.

Cease routing audiovisual data from a first video source to the outputboard.

Continue generating video timing data at the scaler of the output board.

Begin routing audiovisual data from a second video source to the inputboard.

Cease generating image content data upon achieving video lock.

According to aspects of the embodiments, the video distribution systemleverages a backdoor communication bus to prepare downstream devices,such as an output board 310 internal to the switcher device 302 orexternal to the switcher device 302, for a switching event.

Prior to a switching event, the switcher processing unit 318 transmits aprepare signal to downstream devices to prepare for a switching event.Each downstream device then relays the prepare signal to theirdownstream devices until the prepare signal is received at eachnecessary output board 310. For example, downstream devices may compriseadditional switcher devices, output boards or intermediary relaydevices, and output boards 310 may comprise output boxes and outputcards outputting audiovisual data to a video sink.

Output scalers 402 in the output boards 310 then “freeze” the currentvideo in anticipation of the switch by ceasing transmission of scaledlive audiovisual data to the sink and instead generate and outputaudiovisual data comprising a repeated frame of image content data. Therepeated frame of image content data may be a frame of image contentdata received from the first audiovisual source prior to the switchingevent. By generating a repeated frame of image content data from thefirst audiovisual source, the video displayed on the video sink willappear to have momentarily frozen.

The switcher processing unit 318 directs the multiplexer 306 to performthe switching event subsequent to transmission of the prepare signal.The switcher processing unit 318 may direct the multiplexer 306 toperform the switch upon a predefined amount of time after transmittingthe prepare signal or may direct the multiplexer 306 subsequent toconfirming reception of the prepare signal.

The output scaler 402 generates and outputs the repeated frame of imagecontent data until it has achieved video lock with the audiovisual datait receives subsequent to the switching event. By freezing and thenunfreezing the video displayed on the video sink, the output scaler 402achieves the look of an “instant switch” which is aesthetically pleasingto viewers and provides the perception of an instantaneous switch.According to aspects of the embodiments, while the video system maydistribute secure content, such as HDCP protected content, the contentdoes not necessarily need be protected content.

FIG. 8 shows a block diagram of a portion of the switcher device,according to aspects of the embodiments. The multiplexer 306 transmitsan audiovisual data signal from the first input board to a first outputboard 310 a. The multiplexer 306 dynamically switches between the firstinput board and a second input board based on a user control signal thatselects either the first video source or second video source to bedisplayed on the video sink.

The output board may be a card configured for being inserted into theswitcher device or may be external to the switcher device. According toaspects of the embodiments, there may be one or more intermediarydevices between the multiplexer 306 and the output board such asadditional switcher devices and relay devices as shown in the videodistribution system of FIG. 10. The output board comprises a receiver,an output scaler 402, an output processing unit 403 and a transmitter215. As discussed above, the transmitter 215 may be an HDCP transmitter.The receiver 401 is configured to receive audiovisual data routed fromthe first input board or second input board via the multiplexer 306. Thereceiver may be an HDCP receiver configured for receiving HDCP encryptedcontent.

The output scaler 402 receives the audiovisual data from the receiverand is configured to convert the received audiovisual data to a nativeresolution of the video sink. The output board may receive the nativeresolution of the video sink via an EDID channel. Those skilled in theart will recognize that the operation of video scalers embedded in enduser devices are idiosyncratic depending on manufacturer and may performsubstantially below par, resulting in poor video quality and delayedperformance. By converting to the native resolution of the video sink,video processing is minimized in downstream embedded video scalers.

According to aspects of the embodiments, the output scaler 402 of theoutput board 310 is adapted for operating in a pass through mode inwhich the output scaler 402 detects the resolution of the incomingaudiovisual data via the video timing data. The output scaler 402 passesthe incoming audiovisual data through to the transmitter 215 if theaudiovisual data is routed to the output board 310 already at a nativeresolution of the video sink.

The output scaler 402 is further adapted to generate audiovisual datacomprising video timing data and image content data prior to and duringswitching discontinuities. The output scaler 402 may further comprise amemory buffer and a frame buffer for generating and outputting arepeated frame of video to the video sink.

According to aspects of the embodiments, prior to and during a switchingdiscontinuity from a switching event, the output scaler 402 may output arepeated frame of image content data from the audiovisual data receivedfrom the first source. For example, upon receiving the prepare signalfrom the multiplexer 306, the output scaler 402 will “freeze” the videodisplayed on the video sink by generating and outputting a repeatingframe of image content data from the audiovisual data received from thefirst source. The output scaler 402 is configured for continuing togenerate and output audiovisual data comprising video timing data andthe repeated frame of image content data while the switcher deviceceases routing audiovisual data from the first video source and beginsrouting audiovisual data from the second video source.

The output scaler 402 must receive a sufficient amount of audiovisualdata from the second source 104 b prior to outputting live audiovisualdata from the second source 104 b. This is known as achieving videolock. Following a switching discontinuity, the output scaler 402 isfurther configured to generate the video timing data and repeated frameof image content data until video lock is achieved. Upon achieving videolock with the incoming video after the switching discontinuity, theoutput scaler 402 will then “unfreeze” the video by ceasing outputtingthe repeating frame and instead outputting the live scaled video. Byrepeating a frame of video, the user is presented a cleaner and moreaesthetically pleasing switch consisting of a momentarily, and in someinstances imperceptible, frozen screen.

In addition to the aesthetic advantages and perceived reduction inswitching time by the user, aspects of the embodiments reduce theswitching time by maintaining scaler lock in any downstream scalars suchas scalars embedded in video sinks. In HDCP systems switching time isfurther minimized. By outputting a continuous stream of audiovisualdata, more specifically video timing data, to the HDCP transmitter 215,the HDCP link between the output board and the source is maintained asauthenticated during the switch.

The output scaler 402 is adapted to generate image content data inresponse to control signals from the output processing unit 403. Thecommunication interface between the switcher processing unit 318 and theoutput processing unit 403 may be an Ethernet interface. According toaspects of the embodiments, the prepare signal may be a user datagramprotocol (UDP) packet transmitted over the Ethernet interface. However,aspects of the embodiments are not limited to UDP packets transmittedover Ethernet. In other aspects of the embodiments, the interface may bea serial peripheral interface (SPI) or may be an HDMI interfacetransmitting the prepare signal as an info-frame packet.

Upon receiving the user control signal to initiate a switching event andprior to transmitting a switching signal to the multiplexer 306, theswitcher processing unit 318 transmits a prepare signal to the outputprocessing unit 403 via a communication interface. The output processingunit 403 in turn instructs the output scaler 402 to generate a repeatedframe of audiovisual data.

According to aspects of the embodiments, the switcher processing unit318 may broadcast the prepare signal to each connected downstreamdevice. Each downstream device may in turn process and broadcast theprepare signal to each of its connected downstream devices. As will bediscussed below, in further aspects of the embodiments, the switcherprocessing unit 318 may transmit directly to each necessary outputscaler 402. The prepare signal may comprise an address, such as anetwork address of an output card or output box.

The transmitter 215 is configured for converting and encoding theaudiovisual data from the output scaler 402 for transmission to thevideo sink. According to aspects of the embodiments, the transmitter 215is an HDCP transmitter 215. The HDCP transmitter 215, such as an HDMItransmitter 215, converts and encodes the audiovisual data output fromthe output scaler 402 to one or more TDMS signals for transmission tothe video sink over the HDCP interface. According to aspects of theembodiments, the HDMI transmitter 215 comprises an HDCP transmitter 215chip and may further comprise TMDS encoders or decoders and otherHDMI-specific features. The audiovisual data is re-encrypted inaccordance with the shared secret from authentication between the HCDPrepeater and the HDCP sink. The HDCP transmitter 215 receives the nativeresolution and the native refresh of the sink via a DDC of theinterface. The HDCP interface between transmitter 215 and the HDCPreceiver may be HDMI.

FIG. 9 is a flowchart illustrating steps to perform method 900 forreducing the switching time in a video distribution network, accordingto aspects of the embodiments.

In step 901, a switcher device receives audiovisual data at a firstinput board via an AV link between a first video sink and the firstinput board.

In step 902, the switcher device routes audiovisual data from the firstinput board to an output board.

In step 904, the output board transmits audiovisual data to a video sinkover an AV link. According to aspects of the embodiments, the outputboard scales the audiovisual data received from the first input board tothe native resolution of the video sink (step 903) prior to transmittingto the video sink.

In step 905, the processing unit 318 of the switcher device receives acontrol signal to switch from routing audiovisual data from the firstinput board to routing audiovisual data from the second input board.

In step 906, the switcher device processing unit 318 transmits a preparesignal to the output board, indicating that there will be a switchingdiscontinuity.

In step 907, the output board generates image content data, such as arepeating frame of video, in response to receiving the prepare signalfrom the switcher device processing unit 318. The output scaler 402outputs the generated image content data rather than the live imagecontent data being routed to the output board from the multiplexer 306.

In step 908, the multiplexer 306 ceases routing audiovisual data fromthe first input board.

In step 909, the output board continues generating video timing data ata native resolution during the delay between receiving audiovisual datafrom the first input board and receiving audiovisual data from thesecond input board. By outputting a continuous stream of video timingdata, the output board may maintain the authenticity of any securitylink between the output board and the video sink.

In step 910, the switcher device receives audiovisual data at a secondinput board via an AV link between a second video sink and the secondinput board.

In step 911, the switcher device routes audiovisual data from the secondinput board to the output board.

Following step 911 is decision step 915. In decision step 915, it isdetermined whether video lock has occurred. If video lock has occurred(“Yes” path from decision step 915), method 900 proceeds to step 913. Ifvideo lock has not occurred (“No” path from decision step 915), method900 proceeds to step 912. In step 912, the output board continuesgenerating and outputting image content data (i.e. repeating frame ofvideo) until video lock is achieved.

In step 914, the output board transmits live image content data routedfrom the second input board to the video sink over an AV link. Accordingto aspects of the embodiments, the output board scales the audiovisualdata received from the first input board to the native resolution of thevideo sink (step 913) prior to transmitting to the video sink.

The following is a pseudo-code representation of the operation inaccordance with aspects of the embodiments.

Detect a user control signal to switch from a first video source to asecond video source.

Transmit a prepare signal to a processing unit of an output board inresponse to the detection of the user control signal.

Detect the prepare signal at the output board.

Instruct output scaler to generate a repeated frame of image contentdata.

Cease routing audiovisual data from a first video source to the outputboard.

Continue generating video timing data at the output scaler of the outputboard.

Begin routing audiovisual data from a second video source to the inputboard.

Cease generating image content data upon achieving video lock.

According to aspects of the embodiments, the switcher device processingunit 318 is adapted to determine the network topology of the videodistribution network and transmitting an addressed prepare signal toeach desired output device.

Certain video distribution networks, such as those employed on corporatecampuses or educational institutions, may comprise one or more switcherdevices 302 connected in a complex topology. In addition to beingcoupled to one or more output boards 310 (i.e. output cards 310 a,output boxes 310 b), a switcher device 302 may be communicativelycoupled with one or more switcher devices 302 to extend the reach andbreadth of the video distribution network. In addition, a single AVsource may be routed to more than one AV sink. For example, an AV sourcemay be displayed in multiple conference rooms of a corporate facility.In this example, a switcher device may have to route audiovisual datafrom the multiplexer 306 to more than one output board 310.

FIG. 10 is a diagram of a video distribution network according toaspects of the embodiments. The video distribution network 1000comprises a plurality of cascaded switcher devices 302. According toaspects of the embodiments, an output of a first switcher device 302 ais coupled to an input of a second switcher device 302 b and an outputof the second switcher device 302 b is coupled to an input of a thirdswitcher device 302 c.

Each successive device adds delay to the switching times during aswitching event. Consider, as an example, video distribution network1000 in which the first switcher device 302 a receives audiovisual dataat a first input card and routes to a video sink 106 e via an outputcard coupled to a second switcher device 302 b and third switcher device302 c and an output box 310 e. According to aspects of the embodimentsin which the first switcher device processing unit 318 transmits aprepare signal to each of its endpoints (i.e. 310 a, 510 a . . . 510 b),which then process and transmit to each of their endpoints until itreaches the desired endpoint, a noticeable delay will have beenintroduced to the switching process.

To reduce the delay caused by transmission of the prepare signal,according to aspects of the embodiments, each switcher device is adaptedto determine and store the topology of the video distribution network.The switcher devices may determine the topology upon being employed inthe video distribution network, upon other devices joining or leavingthe video distribution network, at periodic time intervals, or at anyother time. The switcher device may determine the topology of the videodistribution network via a network scanning tool or other similartechnology.

Upon receiving the control signal to initiate a switching event andprior to transmitting a switch command to the multiplexer 306, theswitching processing unit 318 transmits a prepare signal addressed toone or more desired endpoints. A desired endpoint is each endpointcomprising a scalar and transmitting audiovisual data to desired sinks.The endpoint may comprise an output board, such as an output card or anoutput box.

While the switcher processing unit 318 must still transmit viaintermediary devices, the switcher processing unit 318 need notbroadcast to all downstream devices. Advantageously, the prepare signaldoes not have to be processed at each intermediary node in the networkwhich reduces latencies and reduces bandwidth.

FIG. 11 is a flowchart illustrating steps of method 1100 for reducingthe switching time in a video distribution network 300, according toaspects of the embodiments.

In step 1101, switcher device 302 receives audiovisual data at a firstinput board via an AV link between a first video sink and the firstinput board.

In step 1102, the switcher device 302 routes audiovisual data from thefirst input board to an output board. The output board may be coupledvia intermediate devices such as other switcher devices and outputboards.

In step 1104, the output board transmits audiovisual data to a videosink over an AV link. According to aspects of the embodiments, theoutput board scales the audiovisual data received from the first inputboard to the native resolution of the video sink (step 1103) prior totransmitting to the video sink.

In step 1105, the processing unit 318 of the switcher device 302receives a control signal to switch from routing audiovisual data fromthe first input board to the output board to routing audiovisual datafrom the second input board to the output board.

In step 1106, the switcher device processing unit 318 determines thepath to the output board including an output of the switcher device 302and a network address of the output board from a stored networktopology. Using the above example, in regard to FIG. 10, to firstswitcher device 302 a may determine that the path to an endpointcomprises a third output board of the switcher device.

In step 1107, the switcher device processing unit 318 transmits aprepare signal comprising the network address of the output board to theoutput board, indicating that there will be a switching event. Theswitcher device transmits the addressed prepare signal to theappropriate downstream node according to the topology.

In step 1108, the output board generates image content data, such as arepeating frame of video, in response to receiving the prepare signalfrom the switcher device processing unit 318. Upon receiving the preparesignal, the output scaler 402 may freeze on a frame of video bycontinuously outputting that frame.

The output scaler 402 outputs the generated image content data ratherthan the live image content data being routed to the output board fromthe multiplexer 306.

In step 1109, the multiplexer 306 ceases routing audiovisual data fromthe first input board.

In step 1110, the output board continues generating video timing data ata native resolution during the delay between receiving audiovisual datafrom the first input board and receiving audiovisual data from thesecond input board. By outputting a continuous stream of video timingdata, the output board maintains the authenticity of the security linkbetween the output board and the video sink.

In step 1111, the switcher device receives audiovisual data at a secondinput board via an AV link between a second video sink and the secondinput board.

In step 1112, the switcher device routes audiovisual data from thesecond input board to the output board.

Following step 1112 is decision step 1116. In decision step 1116, it isdetermined whether video lock has occurred. If video lock has occurred(“Yes” path from decision step 1116), method 1100 proceeds to step 1114.If video lock has not occurred (“No” path from decision step 1116),method 1100 proceeds to step 1113. In step 1113, the output boardcontinues generating and outputting image content data (i.e. repeatingframe of video) until video lock is achieved.

In step 1115, the output board transmits live image content data routedfrom the second input board to the video sink over an AV link. Accordingto aspects of the embodiments, the output board scales the audiovisualdata received from the first input board to the native resolution of thevideo sink (step 1114) prior to transmitting to the video sink.

The following is a pseudo-code representation of the operation inaccordance with aspects of the embodiments.

Detect a user control signal to switch from a first video source to asecond video source.

Determine network address of a desired output card.

Transmit a prepare signal comprising network address to a processingunit 403 of the desired output board in response to the detection of theuser control signal.

Detect the prepare signal at the output board.

Instruct scaler to generate a repeated frame of image content data.

Cease routing audiovisual data from a first video source to the outputboard.

Continue generating video timing data at the scaler of the output board.

Begin routing audiovisual data from a second video source to the inputboard.

Cease generating image content data upon achieving video lock.

FIG. 12 shows a block diagram of the output scaler, according to aspectsof the embodiments. The output scaler comprises a frame rate processingblock 1202, a memory further comprising a frame buffer 1204, an inputscaling block 1206 and an output scaling block 1208. According toaspects of the embodiments, the term block is synonymous with circuit.

The scaler receives input audiovisual data 1201 from the receivercomprising video timing data and image content data. The frame rateprocessing block is adapted to receive the asynchronous input videotiming data 1201 and write the incoming image content data into memory1204. The frame rate processing block 1202 is further adapted to receivethe free-running output video timing data 1211 and read incoming videodata from memory 1204 as required by the output resolution of the scaler402 (i.e. native resolution of the video sink). The frame rateprocessing block 1202 is further adapted to perform frame rateconversion if the input refresh rate and the output refresh rate of theaudiovisual data differ.

The input scaling block 1206 is adapted to receive the asynchronousinput video timing data and perform scaling if required. In certainapplications depending on the input and output setups, input scaling canbe performed prior to frame rate processing according to aspects of theembodiments. According to further aspects of the embodiments, outputscaling can be performed subsequent to frame rate processing. In theseapplications, the output scaling block 1208 receives the free runningoutput video timing data and performs scaling if required.

The free running output timing generator 1210 is adapted to continuouslygenerate free running output video timing data 1211 used to give thedownstream video sink a fixed resolution.

According to aspects of the embodiments in which the output scaler 402generates audiovisual data comprising a repeated frame of image contentdata, the last frame of video received by the output scaler 402 (i.e.the frame to be repeated), is repeatedly read from the memory and framebuffer and output by the output scaler 402. Upon the output scaler 402achieving scaler lock with audiovisual data from the second source, aframe of image content data from audiovisual data received from thesecond source is read from the memory and frame buffer and output by theoutput scaler 402.

Any process descriptions or blocks in flow charts should be understoodas representing modules, segments or portions of code that include oneor more executable instructions for implementing specific logicfunctions or steps in the process. Alternate implementations areincluded within the scope of the aspects of the embodiments in whichfunctions can be executed out of order from that shown or discussed,including substantial concurrence or reverse order, depending on thefunctionality involved, as would be understood by those of skill in theart. Also, steps disclosed as separate may be performed concurrently orcombined, and a step shown as discrete may be performed as two or moresteps. Furthermore, numerical values and disclosures of specifichardware are illustrative rather than limiting. Moreover, while thepreferred embodiment has been disclosed in the context of HDMI, aspectsof the embodiments can be implemented for use with another suitableinterface that uses HDCP, such as DVI or any substantially HDMI-likeinterface. Therefore, aspects of the embodiments should be construed aslimited by only the appended claims.

In this description, various functions and operations can be describedas being performed by or caused by software code to simplifydescription. However, those skilled in the art will recognize what ismeant by such expressions is that the functions result from execution ofthe code by a processor or processing unit, such as a microprocessor.Alternatively, or in combination, the functions and operations can beimplemented using special purpose circuitry, with or without softwareinstructions, such as using application-specific integrated circuit(ASIC) or field-programmable gate array (FPGA). Embodiments can beimplemented using hardwired circuitry without software instructions, orin combination with software instructions. Thus, the techniques arelimited neither to any specific combination of hardware circuitry andsoftware, nor to any particular source for the instructions executed bythe data processing system.

While some embodiments can be implemented in fully functioning computersand computer systems, various embodiments are capable of beingdistributed as a computing product in a variety of forms and are capableof being applied regardless of the particular type of machine ofcomputer-readable media used to actually effect the distribution.

At least some aspects disclosed can be embodied, at least in part, insoftware. That is, the techniques may be carried out in a computersystem or other data processing system in response to itsprocessor/processing unit, such as a microprocessor, executing sequencesof instructions contained in a memory, such as ROM, volatile RAM,non-volatile memory, cache or a remote storage device.

Routines executed to implement the embodiments can be implemented aspart of an operating system, middleware, service delivery platform,software development kit (SDK) component, web services, or otherspecific application, component, program, object, module or sequence ofinstructions referred to as “computer programs”. Invocation interfacesto these routines can be exposed to a software development community asan application programming interface (API). The computer programstypically comprise one or more instructions set at various times invarious memory and storage devices in a computer, and that, when readand executed by one or more processors/processing units in a computer,cause the computer to perform operations necessary to execute elementsinvolving the various aspects.

A machine readable medium can be used to store software and data whichwhen executed by a data processing system causes the system to performvarious methods. The executable software and data can be stored invarious places, including for example ROM, volatile RAM, non-volatilememory and/or cache. Portions of this software and/or data can be storedin any of these storage devices. Further, the data and instructions canbe obtained from centralized servers or peer to peer networks. Differentportions of the data and instructions can be obtained from differentcentralized servers and/or peer-to-peer networks. Different portions ofthe data and instructions can be obtained from different communicationsessions or in a same communication session. The data and instructionscan be obtained in their entirety prior to the execution of theapplications. Alternatively, portions of the data and instructions canbe obtained dynamically, just in time, when needed for execution. Thus,it is not required that the data and instructions be on a machinereadable medium in entirety at a particular instance of time.

Examples of computer-readable media include, but are not limited to,recordable and non-recordable type media, such as volatile andnon-volatile memory devices, read-only memory (ROM), random accessmemory (RAM), flash memory devices, floppy and other removable disks,magnetic disk storage media, optical storage media (e.g. compact discread-only memory (CD ROM), digital versatile discs (DVDs), etc.) amongothers. The instructions may be embodied in digital and analogcommunication links for electrical, optical, acoustical or other formsof propagated signals, such as carrier waves, infrared signals, digitalsignals, etc.

In general, a machine readable medium includes any mechanism thatprovides (i.e. stores and/or transmits) information in a form accessibleby a machine (e.g. a computer, network device, personal digitalassistant, manufacturing tool, any device with a set of one or moreprocessors, etc.).

In various embodiments, hardwired circuitry can be used in combinationwith software instructions to implement the techniques. Thus, thetechniques are neither limited to any specific combination or hardwarecircuitry and software nor to any particular source for the instructionsexecuted by the data processing system.

Although some of the drawings illustrate a number of operations in aparticular order, operations that are not order dependent can bereordered and other operations can be combined, or broken out. Whilesome reordering or other groupings are specifically mentioned, otherswill be apparent to those of ordinary skill in the art and so do notpresent an exhaustive list of alternatives. Moreover, it should berecognized that the stages could be implemented in hardware, firmware,software or any combination thereof.

Although aspects of the embodiments have been described herein withreference to the accompanying drawings, it is to be understood that theaspects of the embodiments are not limited to those precise embodiments,and that various other changes and modifications may be made therein byone skilled in the art without departing from the scope of the appendedclaims.

INDUSTRIAL APPLICABILITY

To solve the aforementioned problems, aspects of the embodiments aredirected towards a unique device in which an output board with an outputscaler 402 minimizes switching delay in a video distribution network byoutputting a continuous stream of audiovisual data during switchingevents.

ALTERNATE EMBODIMENTS

Alternate embodiments may be devised without departing from the spiritor the scope of the aspects of the embodiments. For example, duringswitching events, the output scaler can generate video information suchthat a switching graphic will be displayed on the screen or a colorother than black.

We claim:
 1. A method for switching audiovisual sources in a videodistribution network, the method comprising: (a) receiving firstaudiovisual data at a switching device; (b) transmitting the receivedfirst audiovisual data from the switching device to at least oneaudiovisual data sink; (c) receiving second audiovisual data during aswitching event; (d) transmitting the switched second audiovisual datato the at least one audiovisual data sink; and (e) generating anotification signal a predetermined amount of time prior to the step ofoutputting the switched second audiovisual data.
 2. The method accordingto claim 1, wherein the steps of receiving first and second audiovisualdata comprise: transmitting the first and second audiovisual data froman audiovisual source; receiving the transmitted first and secondaudiovisual data at an input board in the switching device; transmittingthe received first and second audiovisual data from the input board; andreceiving the transmitted first and second audiovisual data from theinput board at a multiplexer in the switching device.
 3. The methodaccording to claim 1, wherein the switching event comprises: a switchfrom receiving audiovisual data from a first audiovisual source toreceiving audiovisual data from a second audiovisual source.
 4. Themethod according to claim 1, wherein the switching event comprises: aswitch from receiving audiovisual data at a first resolution toreceiving audiovisual data at a second resolution.
 5. The methodaccording to claim 1, wherein the switching event comprises: a switchfrom receiving audiovisual data at a first refresh rate to receivingaudiovisual data at a second refresh rate.
 6. The method according toclaim 1, wherein the steps of outputting first and second audiovisualdata comprises: outputting the first and second audiovisual data fromthe multiplexer to an output board; and outputting the first and secondaudiovisual data from the output board to an audiovisual sink.
 7. Themethod according to claim 1, further comprising: determining that anaudiovisual switching event will occur; transmitting a switch signal tothe multiplexer; and notifying the output board that it will receive anoutput from the multiplexer a predetermined amount of time prior totransmitting the switch signal to the multiplexer for the switchingevent.
 8. The method according to claim 7, wherein the step of notifyingcomprises: receiving a control signal at a switcher device processingunit (318) that indicates a switching event from the first audiovisualdata to the second audiovisual data; and transmitting a prepare signalto the output board from the switcher device processing unit prior toswitching from the first audiovisual data to the second audiovisualdata.
 9. The method according to claim 8, further comprising: inresponse to receipt of the prepare signal, generating audiovisual databy a scalar in the output board comprising a repeated frame of imagecontent data during the delay between receiving the first audiovisualdata and receiving the second audiovisual data.
 10. The method accordingto claim 9, wherein the repeated frame of image content data comprises:image content data from the first audiovisual data.
 11. The methodaccording to claim 9, further comprising; transmitting the audiovisualdata to the audiovisual sink by the output board using a securityprotocol link, and maintaining the security protocol link as anauthenticated interface by generating a continuous stream of videotiming data during the switching event.
 12. The method according toclaim 9, wherein the prepare signal comprises: a network address of theoutput board.
 13. The method according to claim 12, further comprising:determining a video distribution network topology.
 14. The methodaccording to claim 13 further comprising: determining a network path tothe output device.
 15. The method according to claim 1, furthercomprising: scaling audiovisual data at the output device to a nativeresolution of the display.
 16. The method according to claim 1, furthercomprising: continuing to generate audiovisual data at the output deviceuntil an amount of audiovisual data sufficient to achieve video lock isreceived from the second audiovisual source.